A radar device radiates a predetermined transmission signal from an antenna as a radio wave, receives a reflected wave reflected by an object by the antenna, and processes this received signal to detect information of the object such as the distance to the object and/or the relative speed of the object, and/or the azimuthal angle of the object. The intensity of the radio wave radiated from the antenna is reduced until the radio wave is received again by the antenna after being reflected by the object; therefore, the intensity of the received signal becomes smaller compared with that of the transmission signal. Particularly, in order to enable detection of an object that has a small reflection rate of radio waves at a greater distance, there is a need to enable processing of the received signals that have small intensity.
Incidentally, in the radar device, signal processing of a transmitting side for generating the transmission signal and radiating the signal from the antenna and signal processing of a receiving side for enabling acquisition of the information of the object from the received signal are carried out, and various noise signals are generated in the radar device along with the signal processing. Particularly, in a radar device attached to a mobile body or the like, a transmitting circuit, which carries out signal processing of the transmitting side, and a receiving circuit, which carries out signal processing of the receiving side, are disposed to be close to each other because of demands for downsizing; therefore, electromagnetic coupling may occur between the transmitting circuit and the receiving circuit, and noise signals may be propagated. In the case in which a radar device is constituted by connecting a plurality of units by multi-terminal connectors, lines (terminals) which conduct various signals are mutually close in the connector unit; therefore, in some cases, electromagnetic coupling occurs among the lines, and the influence of noise signals becomes notable.
In the radar device, the transmitting circuit and the receiving circuit, which process high-frequency signals, are mounted on a high-frequency substrate; and a signal processing unit, which subjects a baseband signal down-converted by a high-frequency circuit to signal processing, and a control unit, which controls the transmitting circuit and the receiving circuit, are mounted on a low-frequency substrate. The high-frequency substrate and the low-frequency substrate are connected to each other by a connector. In the case of such a configuration, a transmission line of the baseband signal and a transmission line of a control signal may be electromagnetically coupled to each other in the connector and cause a noise signal to be mixed in the baseband signal.
In some cases, the transmitting circuit and the receiving circuit, which process the high-frequency signals, and the signal processing unit, which subjects the baseband signal down-converted by the high-frequency circuit to signal processing, are mounted on a single substrate. Also in the case of such a configuration, electromagnetic coupling may occur when the transmission line of the baseband signal and the transmission line of the control signal are close to each other, and noise signals may be mixed in the baseband signal.
In this manner, noise signals may be generated in the radar device due to various factors, and such noise signals may be mixed in the received signals. If the noise signals are mixed in the received signals, there is a problem that signals are detected even without the presence of an object that reflects radio waves, and an object is erroneously detected as a result. Moreover, an amplifier or the signal processing unit may be saturated by the noise signals; and, in this case, there is a problem that the intensity of the received signals cannot be correctly processed, and information of the object is erroneously detected.
As a conventional technique which removes such noise signals, for example, a technique described in Patent Document 1 is known. In a communication processing device described in Patent Document 1, a beat signal demodulated from a received signal is subjected to AD conversion, a signal corresponding to a noise component is extracted from a signal obtained by subjecting the result of AD conversion to high-speed Fourier transformation and is subjected to inverse Fourier transformation, and the result thereof is stored in a memory. Then, the beat signal demodulated from the received signal is subjected to AD conversion, and the signal stored in the memory is then subtracted therefrom to remove the noise component.
As another conventional technique which removes noise signals, in Patent Document 2, a transmitting/receiving signal generating unit, which generates a transmission signal for transmitting a transmitting wave from an antenna and generates a receiving signal from a received wave received by the antenna, and a noise generating unit, which has the same configuration as the transmitting/receiving signal generating unit and generates a noise signal having a reversed phase of the received signal, are provided. A radar device, which is disclosed, generates a receiving signal from which the noise signal is removed by adding the noise signal having the reversed phase to the receiving signal generated by the transmitting/receiving signal generating unit.